1. Field of the Invention
This invention relates to a water-soluble glass water-treating agent of boron-free from its glass composition, and more particularly to a water-treating agent composed of water-soluble glass containing monovalent silver ion effective for the prevention of water putrefaction, formation of slime and growth of algae in water.
2. Prior Art
It was proposed by a Japanese Patent Publication Laid-open No. 210098/1987 to prevent the putrefaction, formation of slime, and growth of algae by removing bacteria and microorganisms from water by treating the water with water-soluble glass composition containing monovalent therein. The present inventors previously proposed in Japanese Patent Application Ser. No. 183055/1986 (Laid-open No. 39692/1988) and U.S. Patent Application Ser. No. 07/311,105 an effective art of wrapping a water-soluble glass water-treating agent in a water-permeable fiber cloth or synthetic resin sheet and steeping the same in water to make Ag+ ion flow out positively and gradually in the water while preventing the glass from becoming difficult of dissolution in the water.
As the composition of the water-soluble glass of the type described above, it is general practice to use one or two kinds of SiO.sub.2, and B.sub.2 O.sub.3 and P.sub.2 O.sub.5 as mesh-forming oxides in combination with one or more than two kinds of Na.sub.2 O, K.sub.2 O, CaO, MgO, BaO and ZnO in the form of mesh-modifying oxides.
But in recent times, some people are anxious about the effects of the water supply system inclusive of drinking water upon the human body (accumulation of boron in the human body when drunk), and the appearance of water-soluble glass free of boron is desired. On the other hand, when the art of making the water-soluble glass is considered in connection with the art of causing the Ag+ ion which is an effective constituent of the glass to flow out positively in the water, more inference cannot be drawn but extensive experiments and studies are necessary for selecting a combination of a mesh-forming oxide with a mesh-modifying oxide and for establishment of the composition range of oxides in bringing water solubility into compatibility with glass formability. The reason is that the phenomenon of the Ag+ ion flowing out of the glass in the water is not theoretically sufficiently elucidated.